In أَثُمَّ رَجَعْتَ؟ hamza introduces a question, thumma indicates sequence with interval, and the past verb retains its subject suffix.
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Hamza before Thumma
The Two Interrogative Particles: Hamza and Hal
In أَثُمَّ رَجَعْتَ؟ hamza introduces a question, thumma indicates sequence with interval, and the past verb retains its subject suffix.